At ISO/ITU-T, JPEG2000 using a discrete wavelet transform (DWT) is being standardized as a successor to JPEG (Joint Photographic Expert Group), which is a standard technology for compression and coding of still images. In JPEG2000, a wide range of image quality, from low bit-rate coding to lossless compression, can be coded highly efficiently, and a scalability function, in which the image quality is gradually raised, can be realized easily. Also, JPEG2000 comes with a variety of functions that the conventional JPEG standard did not have.
As one of the functions of JPEG2000, a ROI coding is standardized, in which a region of interest (Region of Interest; ROI) of an image is coded and transferred in preference to other regions. Because of the ROI coding, when the coding rate has an upper limit, the reproduced image quality of a region of interest can be raised preferentially, and also when a codestream is decoded in sequence, a region of interest can be reproduced earlier with high quality.
Patent Document 1 discloses a technology in which, at the time of a coding, the image quality is enhanced intensively for an image lying in an important range specified by an operator.    [Patent Document 1] Japanese Patent Application Laid-Open No. Hei07-203434.
Nevertheless, in the above-mentioned Patent Document 1, images in a specified range and those in other ranges are coded by their respectively specified image qualities. Accordingly, at the time of a decoding they are limited by their specified image qualities, so that it is difficult to decode them with a various resolutions. Also, it is difficult to achieve a reproduction processing such as one for reproducing only an image of a specified range.